fix(ui): explain silent anno-scale toggles, theme xref empty state

AnnoObjectScaleToggle had three silent no-op paths (no target, locked layer, unknown scale); each now pushes command-line info mirroring the open-path guards. Xref empty-state hardcoded grey now uses muted_style. DD_BOUNDS eviction and attr-clamp changes investigated and deliberately dropped (no reachable defect in either). Tests: anno_scale_toggle_tests cover all three paths (RED: silence). Full suite: 2032 passed / 0 failed / 25 ignored, zero warnings.

src/ui/window/xref_manager.rs

@@ -879,12 +879,7 @@ impl XrefManagerPanel {
             container(
                 text(crate::t!("XREF  No external references in this drawing."))
                     .size(12)
-                    .color(iced::Color {
-                        r: 0.55,
-                        g: 0.55,
-                        b: 0.55,
-                        a: 1.0,
-                    }),
+                    .style(muted_style),
             )
             .center_x(Fill)
             .center_y(Fill)